Personal washing bars such as soap bars have played an important role in hygiene and their routine use has been critical in reducing the spread of communicable diseases. Manufacturers have continuously sought ways to improve the in-use sensory properties and skin compatibility of personal washing bars and to increase their affordability to consumers around the world.
Fatty acid soaps derived from triglycerides still remain the predominant surfactant used in the majority of personal wash bars. The main benefit of such soap bars is their cleaning capacity. Nonetheless consumers perceive other benefits such as amount of lather, thickness of lather, rate of lather formation, speed of rinsing, rate of wear of the soap bar, consistency of the bar, formation of mush, delivery of fragrance and softness of the skin after use.
Consumers around the world view the provision of soft skin after use and delivery of fragrance as key attributes to high quality soap bars. One strategy that has been used to deliver such attributes is the use of synthetic surfactants. Use of high levels of synthetic surfactants, however, can lead to various negative properties. These include significant formation of mush, accelerated rate of wear of the bar during use, and decreased speed of rinsing.
As noted, consumers also desire to improve the delivery of fragrance. This approach usually relies upon increased charges of fragrance in the soap bar composition. Use of high levels of perfume or fragrance can be extremely expensive, especially when compared with the rest of the soap bar ingredients. Additionally, even though higher amounts of fragrance are used, there is often a huge loss of fragrance during storage due, for example, to evaporation of the fragrance.
Examples of approaches based on the above concepts include:
U.S. Pat. No. 6,706,675 discloses a translucent soap bar composition that includes a soap mixture, a polyalkylene glycol, at least one of glycerin and sorbitol, water and optionally, free fatty acid. The soap bar composition exhibits translucent properties. Bars of the subject invention contain less polyethylene glycol (PEG) and the molecular weight of the PEG is typically higher than used in this reference. Larger amounts appear to be required in the reference to create greater translucency (column 6, lines 38-41).
WO 13/076047 discloses soap bars having improved lathering effect by limiting the amounts of myristic acid and using specifically defined ratios of fatty acids.
WO 01/80820 discloses a method for cleansing skin comprising washing with bars comprising predominantly fatty acid soap; free fatty acid and polyalkylene glycol in defined ratios, wherein skin condition is improved as measured by reduced skin damage.
WO 01/80821 discloses bars comprising fatty acid soaps, free fatty acid, polyalkylene glycol and specific salts of protic acid and a process for making the bars.
Further extensive experimentation has revealed that the increased skin softness properties of compositions structured with nonionic polymers combined with short chain free fatty acids and polyols such as glycerol and solid particles is surprisingly related to the levels and relative proportions of such ingredients which are present in the soap mixture.
It was surprisingly found that the combination of specific ranges of percentages by weight of nonionic polymers, (e.g., Polyox WSR-N60K); polyols; short chain free fatty acid (e.g., fatty acids between ten and fourteen carbons); and solid particles were key parameters in delivering improved softness to the skin combined with superior delivery of fragrance. This understanding has now allowed the definition of a composition space for soap bars having a much better delivery of attributes in a narrow range of ingredients, e.g., 0.01-1% of nonionic polymers, 0.1-20% of polyols, 0.01-5% of free fatty acids having lower carbon chain, and 0.1-10% of solid particles, which bars have highly acceptable in-use properties and can be manufactured by high speed extrusion. This technology is the subject of the present invention.